To provide a power unit for a small vehicle capable of reducing the width dimension of a right and a left driving wheels.

This power unit for a small vehicle includes rear wheel shafts 33 supporting a pair of a right and a left driving wheels so that the pair of the right and the left driving wheels swing relative to the vehicle body at the same time in a power transmission case provided in rear of a crank case. This power unit for a small vehicle also includes: support portions 50 to support the driving wheels; and brake hubs portions 51 provided in the rear wheel shafts 33 to limit the rotation of the driving wheels in right and left of the power transmission case. The driving wheels corresponding to the brake hub portions 51 is formed of: inside parts 59 to be fastened to the driving shafts 33; rim portions 61, in which tires 60 are to be installed; and spoke portions 62 connecting them. The size of the spoke portions 62 in the radial direction is formed to radially get over the disposal position of air valves 63 to be installed in the rim portions 61.